78 NAJADAOKAE (PONDWEBD FAMII.V) 



36. P. pectindtus L. Stem filiform^, repeatedly dichotomous ; leaves very 

 narrowly linear or setaceous, attenuate to the apex, 1-iierved wilh a few trans- 

 verse veins ; peduncles filiform ; spikes of 2-6 remote whorls ; fruit obliquely 

 broad-obovoid, compressed, 3.5-4.6 mm. long, rounded on the bade, obscurely 

 ridged on the sides ; embryo spiralhj incurved. — Chiefly in brakish water, e. 

 Que. toB. C, s. along the coast to Fla., and in the interior to Pa., the Great 

 Lake region, Kan., Col., etc. July-Sept. (Cosmop.) 



37. P. interruptus Kitaibel. Similar; leaves usually broader (0.5-2 mm. 

 ■wide) ; edges of the stipules less scarious ; fruit more compressed, sharply keeled. 

 . — Coast of e. N. B. ; Mich. ; probably of wide distrib. July-Sept. (Ku.) 



38. P. Robbinsii Oakes. Stem ascending from a creeping base, rigid, very 

 branching, invested by the bases of the leaves and stipules ; leaves crowded in two 

 ranks, recuroed-spreading, narrow-lanceolate or linear, 7-12 cm. long, acuminate, 

 ciliate-serrulate with translucent teeth, many-nerved ; stipules obtuse when 

 young, their nerves soon becoming bristles ; spikes numerous, loosely few- 

 flowered, on short peduncles ; fruit obloiig-obovoid, keeled with a broadiah wing, 

 acutely beaked ; embiyo stout, ovally annular. — In quiet water, N. B. to B. C, 

 s. to Del., Pa., Ind., Wye, Ida., and Ore. ; rarely fruiting. July-Sept. 



2. r6pPIA L. Ditch Grass 



Flowers 2 or more (approximate on a slender spadix, which is at first inclosed 

 in the sheathing spathe-like base of a leaf), consisting of 2 sessile stamens, each 

 with 2 large and separate anther-cells, and 4 small sessile ovaries, with solitary 

 carapylotropous suspended ovules ; stigma sessile, depressed. Fruit small ob- 

 liquely ovoid pointed drupes, each raised on a slender stalk which appears after 

 flowering ; the spadix itself also then raised on an elongated thread-form 

 peduncle. Embryo ovoid, with a short and pointed plumule from the upper end, 

 by the side of the short cotyledon. — Marine herbs, growing under water, with 

 long and thread-like forking stems, and slender almost capillary alternate leaves 

 sheathing at the base. Flowers rising to the surface at the time of expansion. 

 (Dedicated to H. B. Buppius, a German botanist of the 18th century.) 



1. R. mar'tima L. Leaves linear-capillary ; fruit obliquely erect ; fruiting 

 peduncles capillary (1-3 dm. long) ; stipes 0.5-4 cm. long. — Shallow bays and 

 streams, along the entire coast ; also occasionally in saline places in the interior. 

 (Cosmop.) 



8. ZANNICH^LLIA [Mich.] L. Horned Pondwbed 



Flowers monoecious, sessile, naked, usually both kinds from the same axil; 

 the sterile consisting of a single stamen, with a slender filament bearing a 2-4- 

 celled anther ; the fertile of 2-5 (usually 4) sessile pistils in the same cup-shaped 

 involucre, forming obliquely oblong nutlets in fruit, beaked with a short style, 

 which is tipped by an obliquely disk-shaped or somewhat 2-lobed stigma. Seed 

 orthotropous, suspended, straight. Cotyledon taper, bent and coiled. — Slender 

 branching herbs, growing under water, wilh mostly opposite long and linear 

 thread-form entire leaves, and sheathing membranous stipules. (Named in 

 honor of 0. 0. Zannichelli, a Venetian botanist.) 

 (/ 1. Z. paliistris L. Style at least half as long as the fruit, which is flattish, 

 somewhat incurved, even, or occasionally more or less toothed on the back (not 

 wing-margined in our plant), nearly sessile; or, in var. pedunculXta J. Gay, 

 both the cluster and the separate fruits evidently peduncled. — Ponds and slow 

 streams, chiefly brackish, throughout N. A. July. (Cosmop.) 



4. ZOSXfeRA L. Grass Wrack. Eel Grass 



Flowers monoecious; the two kinds naked and sessile and alternately ar- 

 ranged in two rows on the midrib of one side of a linear leaf-like spadix, which 

 is hidden in a long and sheath-like base of a leaf (sixi.the) ; the sterile flowei-s 

 consisting of single ovate or oval l-ci'lled sessile anthcra, as large as the ovaries. 



